JP5566775B2 - Tape substrate for superconducting wire and superconducting wire - Google Patents

Description

  The present invention relates to a tape substrate and a superconducting wire for a superconducting wire used in superconducting equipment such as a superconducting cable and a superconducting magnet, and more particularly to a configuration of an intermediate layer formed on a metal substrate.

Conventionally, RE-based superconductors (RE: rare earth elements) are known as a type of high-temperature superconductor that exhibits superconductivity at a liquid nitrogen temperature (77 K) or higher. In particular, an yttrium-based superconductor represented by the chemical formula YBa ₂ Cu ₃ O _7-y (hereinafter, Y-based superconductor or YBCO) is representative.
A superconducting wire using a Y-based superconductor (hereinafter referred to as a Y-based superconducting wire) is generally an intermediate layer on a tape-shaped metal substrate, a layer composed of a Y-based superconductor (hereinafter referred to as a Y-based superconducting layer), a stabilization layer. Have a laminated structure formed in order. This Y-based superconducting wire is formed, for example, by forming a biaxially oriented intermediate layer on a low-magnetic non-oriented metal substrate (for example, Hastelloy (registered trademark)), and on this intermediate layer, a pulse laser deposition method (PLD). : Pulsed Laser Deposition), MOCVD: Metal Organic Chemical Vapor Deposition (MOCVD), etc., to produce a Y-based superconducting layer. Below, the long tape base material comprised with a metal substrate and an intermediate | middle layer is called the tape base material for superconducting wires.

  It is known that the current-carrying characteristics of such a superconducting wire greatly depend on the crystal orientation of the superconductor, particularly the biaxial orientation. Therefore, in order to obtain a superconducting layer having high biaxial orientation, it is necessary to improve the crystallinity of the intermediate layer serving as a base. One of the methods is ion beam assisted deposition (IBAD) (for example, Patent Documents 1 and 2). The IBAD method is a method in which an alignment layer is formed by depositing vapor deposition particles from a vapor deposition source on a film formation surface while irradiating an assist ion beam obliquely with respect to the film formation surface. In the IBAD method, since high biaxial orientation is obtained with a thin film, MgO, which is a rock salt type, is used as a vapor deposition source and has become the mainstream of development. Hereinafter, the MgO layer formed by the IBAD method is referred to as an IBAD-MgO layer.

In order to realize high biaxial orientation in the IBAD-MgO layer, the undercoat smoothness and low reactivity with MgO are required. Therefore, immediately below the IBAD-MgO layer, there is a bed layer made of a material capable of forming an amorphous film such as yttrium oxide (Y ₂ O ₃ ) or GZO (Gd ₂ Zr ₂ O ₇ ) that promotes the orientation of IBAD-MgO. It is formed.
On the other hand, in order to obtain high current-carrying characteristics in the superconducting wire, it is necessary to prevent the diffusion of cations (Ni, Mo, Mn, etc.) from the metal substrate to the superconducting layer. Therefore, in general, a barrier layer (diffusion suppression) made of a material such as aluminum oxide (Al ₂ O ₃ ), GZO, YSZ (yttrium stabilized zirconia), chromium oxide (Cr ₂ O ₃ ) between the bed layer and the metal substrate. Layer) is interposed.
In addition, a cap layer made of CeO ₂ or the like is formed on the IBAD-MgO layer in order to protect the IBAD-MgO layer that easily reacts with the atmosphere and to enhance lattice matching with the superconducting layer (for example, YBCO). .

As described above, GZO can promote the orientation of IBAD-MgO and also functions as a barrier layer. Therefore, GZO is promising as a constituent material of the bed layer. Patent Document 3 discloses a tape substrate for a superconducting wire having a laminated structure of CeO ₂ cap layer / IBAD-MgO alignment layer / GZO bed layer / metal substrate.

Japanese Patent Laid-Open No. 4-331895 JP 2007-532775 A JP 2010-86666 A

  However, the GZO bed layer may be crystallized by heat treatment for forming the substrate surface layer, and in this case, the function of promoting the orientation of the IBAD-MgO layer is impaired, which causes a decrease in the degree of orientation ( If the base is amorphous, the IBAD-MgO layer is easier to align). When the degree of orientation of the IBAD-MgO layer is reduced, high current conduction characteristics cannot be obtained in the superconducting wire. For example, when the IBAD-MgO layer is formed on the GZO bed layer without heat treatment, the orientation degree Δφ is 6 °, whereas when the IBAD-MgO layer is formed after heat treatment. Experimental results show that the degree of orientation Δφ decreases to 7 °.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a technique capable of improving the current-carrying characteristics of a superconducting wire.

The invention according to claim 1 is a metal substrate;
A bed layer made of nesosilicate formed on the metal substrate;
An alignment layer formed by ion beam assisted deposition on the bed layer ,
A tape base material for a superconducting wire , wherein a substrate surface layer made of an oxide of a constituent element of the metal substrate is formed at an interface between the metal substrate and the bed layer .

  According to a second aspect of the present invention, in the tape substrate for a superconducting wire according to the first aspect, the bed layer has an amorphous surface in the film forming step of the alignment layer.

The invention according to claim 3, in superconducting wire tape substrate according to claim 1 or 2, wherein the substrate surface layer, I Ri is formed is subjected to predetermined heat treatment after forming the bed layer It is characterized by being.

  The invention according to claim 4 is the tape substrate for a superconducting wire according to any one of claims 1 to 3, wherein the bed layer has a thickness of 10 to 500 nm.

The invention according to claim 5 is the tape substrate for a superconducting wire according to any one of claims 1 to 4, wherein the bed layer is composed of ZrSiO ₄ , HfSiO ₄ , ThSiO ₄ , or USiO _4. It is characterized by that.

Invention according to claim 6, configured in a superconducting wire tape base material according to any one of claims 1 to 5, wherein the alignment layer, MgO, _GZO, CeO 2, YSZ, or NbO It is characterized by that.

  A seventh aspect of the present invention is the tape substrate for a superconducting wire according to any one of the first to sixth aspects, further comprising a cap layer formed on the alignment layer.

The invention according to claim 8 is the tape substrate for a superconducting wire according to claim 7, wherein the cap layer is made of CeO ₂ , YSZ, LaMnO ₃ , or SrTiO ₃ .

  The invention according to claim 9 is a superconducting wire formed by forming a superconducting layer on the surface of the tape substrate for superconducting wire according to any one of claims 1 to 8.

  According to the present invention, since the surface of nesosilicate becomes amorphous in the step of forming the alignment layer, the degree of alignment of the alignment layer formed on the bed layer made of nesosilicate increases. Therefore, it is possible to improve the energization characteristics of the superconducting wire.

It is a figure which shows the laminated structure of the superconducting wire which concerns on embodiment. It is a figure which shows the structure of the tape base material for superconducting wires which concerns on embodiment. It is a figure which shows the manufacturing process of the tape base material for superconducting wires which concerns on embodiment.

Hereinafter, embodiments of the present invention will be described in detail.
FIG. 1 is a view showing a laminated structure of a superconducting wire 1 according to the present embodiment.
As shown in FIG. 1, the Y-based superconducting wire 1 has a laminated structure in which an intermediate layer 20, a superconducting layer 30, and a stabilizing layer 40 are sequentially formed on a tape-like metal substrate 10. The tape-shaped metal substrate 10 and the intermediate layer 20 in FIG. 1 constitute the superconducting wire tape base material 2 according to the present invention.

  In the present embodiment, the metal substrate 10 is a low-magnetic non-oriented metal substrate (for example, Hastelloy (registered trademark)). The intermediate layer 20 includes a bed layer and an alignment layer, and is formed in order to achieve high biaxial alignment in the superconducting layer 30. The superconducting layer 30 is a Y-based superconducting layer made of a Y-based superconductor, and is formed by, for example, the MOCVD method. On the upper surface of the superconducting layer 30, a stabilizing layer 40 made of silver is formed by sputtering, for example.

FIG. 2 is a view showing the structure of the superconducting wire tape base material 2 according to this embodiment. Moreover, the film-forming process of the tape base material 2 for superconducting wires is shown in FIG.
As shown in FIG. 2, the intermediate layer 20 includes a bed layer 21, an alignment layer 22, and a cap layer 23.

The bed layer 21 is a layer for promoting the orientation of the orientation layer 22 and preventing the constituent elements of the metal substrate 10 from diffusing, and has a thickness of 10 to 500 nm. In the present embodiment, the bed layer 21 is made of a nesosilicate having a high oxygen permeability. For example, while the filling rate of GZO is 0.68, the filling rate of ZrSiO ₄ , which is a nesosilicate, is 0.63, and oxygen easily permeates.
The bed layer 21 is formed by RF sputtering, for example (step S101 in FIG. 3). The film formation conditions at this time are set as appropriate depending on the film thickness of the bed layer 21 and the like. For example, RF sputtering output: 100 to 500 W, wire conveyance speed: 10 to 100 m / h, film formation temperature: 20 to 500 ° C. It is said.

  The alignment layer 22 is a polycrystalline thin film made of MgO for aligning the crystals of the superconducting layer 30 in a certain direction, and has a film thickness of 3.0 to 10 nm. The alignment layer 22 is formed by an IBAD method in which vapor deposition particles from a vapor deposition source (MgO) are deposited on the film formation surface while irradiating an assist ion beam obliquely with respect to the film formation surface (step in FIG. 3). S103). The film formation conditions at this time are appropriately set depending on the film thickness of the alignment layer 22 and the like. For example, assist ion beam voltage: 800 to 1500 V, assist ion beam current: 80 to 350 mA, assist ion beam acceleration voltage: 200 V, RF sputtering output: 800 to 1500 W, wire material conveying speed: 80 to 500 m / h, film forming temperature: 100 to 300 ° C.

  The cap layer 23 is a layer for protecting the alignment layer 22 and improving lattice matching with the superconducting layer 30 and has a film thickness of 10 to 500 nm. The cap layer 23 is formed by sputtering, for example (step S104 in FIG. 3). The film formation conditions at this time are appropriately set depending on the film thickness of the cap layer 23 and the like. For example, RF sputtering output: 100 to 1000 W, wire material conveyance speed: 5 to 50 m / h, film formation temperature: 500 to 600 ° C. It is said.

In the superconducting wire tape base material 2, a substrate surface layer 11 made of an oxide of a constituent element of the metal substrate 10 (for example, Cr ₂ O ₃ ) is formed at the interface between the metal substrate 10 and the bed layer 21. Yes. By forming the substrate surface layer 11, it is possible to prevent the intermediate layer 20 from being peeled off when the superconducting layer 30 is formed.
The substrate surface layer 11 is formed by performing a predetermined heat treatment over the entire length of the superconducting wire tape base material 2 after forming the bed layer 21 on the metal substrate 10 (step S102 in FIG. 3). The heat treatment conditions at this time are appropriately set according to the thickness of the bed layer 21 and the thickness of the substrate surface layer 11 to be formed. For example, when the thickness of the bed layer 21 is 100 nm and the thickness of the substrate surface layer 11 is 50 nm, the heat treatment conditions are 500 ° C. and 0.5 hours (wire conveyance speed 1.5 m / h).

  As described above, the superconducting wire tape base material 2 according to the embodiment is formed by the IBAD method on the metal substrate 10, the bed layer 21 made of nesosilicate formed on the metal substrate 10, and the bed layer 21. The alignment layer 22 is provided. Further, by performing a predetermined heat treatment after forming the bed layer 21, the substrate surface layer 11 made of an oxide of a constituent element of the metal substrate 10 is formed at the interface between the metal substrate 10 and the bed layer 21.

Since the nesosilicate is maintained in an amorphous state even at a high temperature of 500 ° C., it is difficult to crystallize in the heat treatment step for forming the substrate surface layer 11. Even if it is crystallized in the heat treatment step, it is known that nesosilicate is amorphously transferred by ion beam irradiation.
On the other hand, when the bed layer 21 is composed of GZO, it has been confirmed that the crystallization is partially performed in the heat treatment step for forming the substrate surface layer 11. Further, it has been confirmed that the surface of the bed layer is crystallized when the assist ion beam is irradiated in the film forming process of the alignment layer 22 and Ar ⁺ ions collide with the film forming surface.
That is, in this embodiment, since the surface of the bed layer 11 is amorphous in the film forming process of the alignment layer 22, the degree of alignment of the alignment layer 22 formed thereon is increased. Therefore, it is possible to improve the energization characteristics of the superconducting wire.

  In addition, since the bed layer 21 is made of nesosilicate having a high oxygen permeability, oxygen easily passes through the bed layer 21 and reaches the metal substrate 10. Therefore, if the conditions such as the thickness of the bed layer 21, the thickness of the substrate surface layer 11 to be formed, and the heat treatment temperature are the same, the heat treatment time is shortened compared to the case where the bed layer 21 is made of GZO (wire material conveyance). Speed up). As a result, productivity can be improved and cost reduction of the superconducting wire can be achieved.

  Since the bed layer 21 undergoes amorphous transition in the film formation process of the alignment layer 22 and may be crystallized in the heat treatment process for forming the substrate surface layer 11, the heat treatment temperature can be further increased. Thereby, heat processing time can further be shortened.

[Example]
In the example, the bed layer 21 made of ZrSiO4, which is a nesosilicate, was formed on the tape-shaped Hastelloy substrate 10 with a film thickness of 8, 10, 50, 100, 200, 300, 500, 600 nm. After the bed layer 21 was formed, the substrate surface layer 11 was formed by performing a heat treatment at 500 ° C. for 0.5 hour. At this time, the film thickness of the substrate surface layer 11 was 400, 300, 120, 80, 50, 30, 10, and 5 nm, respectively.
Then, an alignment layer (IBAD-MgO layer) 22 made of MgO was formed on the bed layer 21 with a film thickness of 5 nm, and a cap layer 23 made of CeO ₂ was formed thereon with a film thickness of 200 nm. A superconducting layer 30 and a stabilization layer 40 were formed on the obtained tape substrate 2 for superconducting wire, and a superconducting wire 1 was produced.

When the thickness of the bed layer 21 was 10 to 500 nm, no peeling of the intermediate layer 20 was observed in any film thickness of the bed layer 21 in the superconducting layer 30 deposition process. In addition, Auger analysis of the superconducting layer 30 and the intermediate layer 20 was performed to examine the diffusion state of cations from the Hastelloy substrate 10 to the superconducting layer 30, and as a result, representative Ni and Cr were not detected as cations.
Further, with respect to the obtained superconducting wire 1, the critical current in liquid nitrogen was measured with a voltage definition of 1 μV / cm by a four-terminal method. As a result, the critical current value was 200 A or more, and good Ic characteristics were obtained.

When the thickness of the bed layer 21 was 8 nm, no peeling of the intermediate layer 20 was observed in the superconducting layer 30 deposition process, but trace amounts of Ni and Cr were detected in the cap layer 23 by Auger analysis. . Moreover, the critical current value of the obtained superconducting wire 1 was 140A.
In the case where the thickness of the bed layer 21 is 8 nm, since the thickness of the bed layer 21 is too thin, the irradiated Ar ⁺ ions penetrate the bed layer 21 or stir the bed layer 21 to form the underlying metal. This is probably because the substrate 10 was exposed and the function of the bed layer to promote the orientation of the orientation layer 22 was impaired.

When the thickness of the bed layer 21 was 600 nm, peeling of the intermediate layer 20 was observed in the film forming process of the superconducting layer 30, and trace amounts of Ni and Cr were detected in the superconducting layer 30 by Auger analysis. Moreover, the critical current value of the obtained superconducting wire 1 was 150A.
When the thickness of the bed layer 21 is 600 nm, the thickness of the bed layer 21 is too thick to make it difficult for oxygen to pass through the bed layer 21, reducing the amount of oxygen supplied to the metal substrate 10, and the substrate surface layer 11. It was considered that the intermediate layer was partially peeled because it was not formed sufficiently. That is, if the thickness of the bed layer 21 is too large, the film formation time of the bed layer 21 itself increases (the wire conveyance speed during film formation decreases), and the heat treatment time for forming the substrate surface layer 11 also increases. Therefore, productivity is reduced and manufacturing costs are increased. Further, as the bed layer 21 is thickened, the wire may be warped due to accumulated strain.

  From the example, it was confirmed that the bed layer 21 functioned effectively as the bed layer 21 without significantly reducing the productivity by setting the thickness of the bed layer 21 to 10 to 500 nm. In particular, it is desirable that the bed layer 21 has a thickness of about 50 nm. In this case, when the alignment layer 22 is formed, it can function reliably as a bed layer, and the oxygen supply to the metal substrate 10 is sufficiently performed, so that the substrate surface layer 11 sufficient to prevent peeling is efficiently used. Can be well formed.

As mentioned above, although the invention made by this inventor was concretely demonstrated based on embodiment, this invention is not limited to the said embodiment, It can change in the range which does not deviate from the summary.
For example, in the tape substrate 2 for a superconducting wire, the cap layer 23 can be composed of one or a combination of CeO ₂ , YSZ, LaMnO ₃ (LMO), or SrTiO ₃ (STO), Alternatively, the cap layer 23 may not be formed.
In addition, the alignment layer 22 can be formed of a single layer of IBAD-MgO or a composite layer in which self-oriented Epi-MgO is epitaxially grown on the IBAD-MgO by the PLD method or the like.
That is, as the main laminated structure of the superconducting wire tape base material 2 provided with the bed layer made of ZrSiO ₄ which is a nesosilicate, the structure shown in Table 1 can be considered. In Table 1, when attention is paid to the characteristics of the tape substrate 2 for superconducting wire and the number of film forming steps, No. 1 is the simplest configuration including the cap layer 23. The laminated structure 1 (the laminated structure shown in the embodiment) is optimal.

Although not shown in Table 1, as the Nesokei salt constituting the bed layer 21, other ZrSiO _4, it can be applied HfSiO _4, ThSiO 4, or USIO _4. The alignment layer 22 can be composed of any one of GZO, CeO ₂ , YSZ, and NbO in addition to MgO. For the metal substrate 10, a non-oriented metal substrate other than Hastelloy, for example, SUS304 can be applied.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

10 Metal substrate 20 Intermediate layer 21 Bed layer (Nesosilicate, ZrSiO ₄ )
22 Alignment layer (IBAD-MgO)
23 Cap layer (CeO ₂ )
30 Superconducting layer (YBCO)
40 Stabilization layer

Claims (9)

A metal substrate;
A bed layer made of nesosilicate formed on the metal substrate;
An alignment layer formed by ion beam assisted deposition on the bed layer ,
A tape base material for a superconducting wire , wherein a substrate surface layer made of an oxide of a constituent element of the metal substrate is formed at an interface between the metal substrate and the bed layer .   The tape substrate for a superconducting wire according to claim 1, wherein the bed layer has an amorphous surface in the step of forming the alignment layer. The substrate surface layer, a superconducting wire tape substrate according to claim 1 or 2, characterized in that it is formed Ri by the performing predetermined heat treatment after forming the bed layer.   4. The superconducting wire tape substrate according to claim 1, wherein the bed layer has a thickness of 10 to 500 nm. 5. The bed _{layer, ZrSiO 4, HfSiO 4, ThSiO} 4, or USiO superconducting wire tape substrate according to claim 1, any one of 4, characterized in that it is composed of _4. The alignment _{layer, MgO, GZO, CeO 2,} YSZ, or a superconducting wire tape substrate according to any one of claims 1 5, characterized in that it is composed of NbO.   It has a cap layer formed on the said orientation layer, The tape base material for superconducting wires as described in any one of Claim 1 to 6 characterized by the above-mentioned. The cap _{layer, CeO 2, YSZ, LaMnO 3} , or a superconducting wire tape substrate according to claim 7, characterized in that it is composed of SrTiO _3.   A superconducting wire formed by forming a superconducting layer on the surface of the tape substrate for a superconducting wire according to any one of claims 1 to 8.

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